<?php
/**
 * 一致性哈希memcache分布式，采用的是虚拟节点的方式解决分布均匀性问题,查找节点采用二分法快速查找
 * the last known user to change this file in the repository<$LastChangedBy: nash.xiong [  DISCUZ_CODE_0  ]gt;
 * @author nash.xiong <nash.xiong@gmail.com>
 * @copyright Copyright &copy; 2003-2012 phpd.cn
 * @license 
 */
class memcacheHashMap {

  private $_node = array();
  private $_nodeData = array();
  private $_keyNode = 0;
  private $_memcache = null;
  
  //每个物理服务器生成虚拟节点个数 [注：节点数越多，cache分布的均匀性越好，同时set get操作时，也更耗资源，10台物理服务器，采用200较为合理]
  private $_virtualNodeNum = 200; 
  
  private function __construct() {
      /* 放入配置文件 */
      $config = array(
                '127.0.0.1:11211',
                '127.0.0.1:11212',
                '127.0.0.1:11213',
                '127.0.0.1:11214',
                '127.0.0.1:11215'
              );
              
      if (!$config) throw new Exception('Cache config NULL');
      foreach ($config as $key => $value) {
        for ($i = 0; $i < $this->_virtualNodeNum; $i++) {
          $this->_node[sprintf("%u", crc32($value . '_' . $i))] = $value . '_' . $i;
        }
      }
      ksort($this->_node);
  }

  private function __clone(){}
  
  /**
   * 单例，保证只有一个实例
   */
  static public function getInstance() {
      static $memcacheObj = null;
      if (!is_object($memcacheObj)) {
        $memcacheObj = new self();
      }
      return $memcacheObj;
  }
  
  /**
   * 根据key做一致性hash后连接到一台物理memcache服务器
   * @param string $key
   */
  private function _connectMemcache($key) {
      $this->_nodeData = array_keys($this->_node);
      $this->_keyNode = sprintf("%u", crc32($key));
      $nodeKey = $this->_findServerNode();
      //如果超出环，从头再用二分法查找一个最近的，然后环的头尾做判断，取最接近的节点
      if ($this->_keyNode > end($this->_nodeData)) {
        $this->_keyNode -= end($this->_nodeData);
        $nodeKey2 = $this->_findServerNode();
        if (abs($nodeKey2 - $this->_keyNode) < abs($nodeKey - $this->_keyNode))$nodeKey = $nodeKey2;
      }
      var_dump($this->_node[$nodeKey]);
      list($config, $num) = explode('_', $this->_node[$nodeKey]);
      if (!$config) throw new Exception('Cache config Error');
      if (!isset($this->_memcache[$config])) {
        $this->_memcache[$config] = new Memcache;
        list($host, $port) = explode(':', $config);
        $this->_memcache[$config]->connect($host, $port);
      }
      return $this->_memcache[$config];
  }
  
  /**
   * 采用二分法从虚拟memcache节点中查找最近的节点
   * @param unknown_type $m
   * @param unknown_type $b
   */
  private function _findServerNode($m = 0, $b = 0) {
    $total = count($this->_nodeData);
    if ($total != 0 && $b == 0) $b = $total - 1;
    if ($m < $b){
      $avg = intval(($m+$b) / 2);
      if ($this->_nodeData[$avg] == $this->_keyNode) return $this->_nodeData[$avg];
      elseif ($this->_keyNode < $this->_nodeData[$avg] && ($avg-1 >= 0)) return $this->_findServerNode($m, $avg-1);
      else return $this->_findServerNode($avg+1, $b);
    }
      if (abs($this->_nodeData[$b] - $this->_keyNode) < abs($this->_nodeData[$m] - $this->_keyNode))return $this->_nodeData[$b];
      else return $this->_nodeData[$m];
  }
  
  public function set($key, $value, $expire = 0) {
      return $this->_connectMemcache($key)->set($key, json_encode($value), 0, $expire);
  }
  
  public function add($key, $value, $expire = 0) {
      return $this->_connectMemcache($key)->add($key, json_encode($value), 0, $expire);
  }
  
  public function get($key) {
      return json_decode($this->_connectMemcache($key)->get($key), true);
  }
  
  public function delete($key) {
      return $this->_connectMemcache($key)->delete($key);
  }
  
}

$runData['BEGIN_TIME'] = microtime(true);
//测试一万次set加get
for($i=0;$i<10000;$i++) {
  $key = md5(mt_rand());
  $b = memcacheHashMap::getInstance()->set($key, time(), 10);
}

var_dump(number_format(microtime(true) - $runData['BEGIN_TIME'],6));
$runData['BEGIN_TIME'] = microtime(true); $m= new Memcache;
$m->connect('127.0.0.1', 11211); 
for($i=0;$i<10000;$i++) {
  $key = md5(mt_rand());
  $b = $m->set($key, time(), 0, 10);
}
var_dump(number_format(microtime(true) - $runData['BEGIN_TIME'],6));
//测试结果，采用一致性哈希分布效率比原生单台速度相差5倍左右
